Mechanical refrigeration systems, and related heat transfer devices, such as heat pumps and air conditioners, using refrigerant liquids are well known in the art for industrial, commercial and domestic uses. Chlorofluorocarbons (CFCs) were developed in the 1930s as refrigerants for such systems. However, since the 1980s the effect of CFCs on the stratospheric ozone layer has become the focus of much attention. In 1987, a number of governments signed the Montreal Protocol to protect the global environment, setting forth a timetable for phasing out the CFC products. CFCs were replaced with more environmentally acceptable materials that contain hydrogen, namely the hydrochlorofluorocarbons (HCFCs).
One of the most commonly used hydrochlorofluorocarbon refrigerants was chlorodifluoromethane (HCFC-22). However, subsequent amendments to the Montreal protocol accelerated the phase out of the CFCs and also scheduled the phase-out of HCFCs, including HCFC-22.
In response to the requirement for a non-flammable, non-toxic alternative to the CFCs and HCFCs, industry has developed a number of hydrofluorocarbons (HFCs) which have zero ozone depletion potential. R-134a (1,1,1,2-tetrafluoroethane) was adopted for various heat exchange applications, including refrigeration applications such as medium temperature refrigeration systems and vending machines, as well as heat pumps and chillers, as it does not contribute to ozone depletion.
However, R-134a has a Global Warming Potential (GWP) of about 1430 (according to IPCC (2007) Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. S. Solomon et al, Cambridge University Press. Cambridge, United Kingdom p 996). There is therefore a need in the art for the replacement of R-134a with a more environmentally acceptable alternative.
It is understood in the art that replacement heat transfer fluids must possess a mosaic of properties depending on the particular application. For many of the applications which involve the cooling or heat of air to which members of public are intended to be exposed, that mosaic will generally include excellent heat transfer properties, chemical stability, low or no toxicity, non-flammability and/or lubricant compatibility amongst others. The identification of a heat transfer fluid meeting all of these requirements is not trivial.
Non-flammability is considered to be an important, and in some cases, an essential property for many heat transfer applications Thus, it is frequently beneficial to use compounds in such compositions, which are non-flammable. As used herein, the term “non-flammable” refers to compounds or compositions which are determined to be non-flammable in accordance with ASTM standard E-681-2001 at conditions described in ASHRAE Standard 34-2013 and described in Appendix B1 to ASHRAE Standard 34-2013.
However, non-flammability is generally understood to be inversely correlated to low GWP. For example, while R-134a is classed as a non-flammable (i.e. class 1) refrigerant, it has a high GWP of about 1430. In contrast, while R152a (1,1-difluoroethane) has a GWP of about 124, it is classed as a flammable (i.e. a class 2) refrigerant. Thus, it is generally difficult to provide a refrigerant which is non-flammable, and which has a low GWP, that is, a GWP of not greater than about 150.